Seat belt tightening device

ABSTRACT

An object of the present invention is to provide a seat belt tightening device including a driving unit having excellent properties which assures that an intensity of webbing tightening power and a quantity of webbing tightening activity can easily be increased, and moreover, acceptable webbing tightening properties can be obtained with the seal belt tightening device. A driving unit 4 for a pretensioner disposed on one side wall of a retractor base 18 includes a pair of gas generators 8 and 9 which are arranged on the base end side of a cylinder 5. At the time of vehicle collision, a piston 6 slidably received in the cylinder 5 is driven by the explosion pressure derived from explosion of an explosive filled in both the gas generators 8 and 9, whereby a webbing winding shaft is rotated in such a direction that the loosened state of a seat belt can be eliminated.

BACKGROUND OF THE INVENTION

The present invention relates generally to a seat belt tightening device(serving as a pretensioner) for eliminating the loosened state of awebbing which arises at the time of vehicle collision, and also to aseat belt apparatus having the same. More particularly, the presentinvention relates to improvement of a seat belt tightening device of theforegoing type including a driving unit wherein a piston displaceablyreceived in a cylinder is driven by gas pressure with the aid of thedriving unit so as to allow a certain intensity of tension to be appliedto the webbing, and also to a seat belt apparatus having the same.

With a conventional seat belt apparatus operable for assuring safety ofpassengers sitting on a seat in a vehicle, since there is a tendencythat an intensity of winding power given by a retractor is reduced forthe purpose of attenuating uncomfortablity felt by each passenger whenhe puts on a webbing around his body, an extent of loosening of a seatbelt caused when he puts on it about his body is unavoidably increased,resulting in effective and safe restricting of each passenger failing tobe achieved due to the delayed tightening of the seat belt extendingabout his body.

In view of the foregoing malfunction of the conventional seat beltapparatus, a proposal has been made with respect to a seat belttightening device incorporated in a seat belt apparatus wherein the seatbelt tightening device is instantaneously retracted together with abuckle to assume the operative state by quickly pulling a webbing at thetime of an occurrence of emergency such as vehicle collision or the likeso as to allow the webbing to be tightened in order to eliminate theloosened state of the seat belt.

To facilitate understanding of the present invention, a typicalconventional retractor having a pretensioner attached thereto willbriefly be described below with reference to FIG. 9.

A retractor 240 shown in FIG. 9 includes a winding reel having a webbing216 wound thereabout in the laminated structure in such a manner as toenable it to be quickly wound and unwound, and a pretensioner 243serving as a seat belt tightening device for rotating a winding shaftfor the webbing 216 in such a direction that the loosened state of aseat belt can be eliminated is arranged on one side wall of a retractorbase 242 of the retractor 240 having a substantially U-shaped sectionalcontour. The pretensioner 243 serves to apply a certain intensity oftension to a wire 247 wound about a pulley (not shown) mounted on thewinding shaft at one end of the latter wherein the wire 247 is used as apower transmission member. With this construction, the wire 247 isretractively driven at the time of an occurrence of emergency such asvehicle collision or the like in such a direction that the winding shaftis rotated in the webbing winding direction, whereby the webbing 216extending about a passenger's body is quickly retracted in the retractor240. To this end, the retractor 240 includes a driving unit 241 forapplying a certain intensity of tension to the wire 247.

The driving unit 241 is composed of a piston 246 connected to one end ofthe wire 247, a cylinder 245 in which the piston 246 is slidablyreceived, and a gas generator 244 connectably communicated with thecylinder 245. An ignition heater and an explosive are received in thegas generator 244. In response to a detection signal, outputted from acollision sensor, the ignition heater is turned on to generate heat,causing the explosive to be exploded to generate gas. When the piston246 is slidably driven in the cylinder 245 in the upward direction bythe expansion pressure of the gas generated in the gas generator 244,the winding shaft is driven in the webbing winding direction so that thewebbing 216 extending about the passenger's body is quickly retracted inthe retractor 240, resulting in the loosened state of the seat beltbeing eliminated.

In addition to the aforementioned pretensioner, a mechanical typepretensioner is also put in practical use to serve in such a manner asto eliminate the loosened state of a seat belt by instantaneouslyretracting a buckle in the webbing stretching direction. This mechanicaltype pretensioner includes a weight adapted to move in response to anacceleration induced by shock and a trigger unit for releasing acompression spring from the preliminarily compressed state in operativeassociation with the weight. With the mechanical type pretensionerconstructed in that way, a webbing extending about a passengers body isretracted in a driving unit by transmitting the restorative resilientpower of the compression spring directly or indirectly to a buckle.

To raise up safety of each passenger with the conventional seat beltapparatus at the time of an occurrence of vehicle collision, it isnecessary that the passenger is intensely restricted on his seat byintensifying the webbing tightening force of the pretensioner andincreasing a quantity of webbing tightening activity. However, since thepretensioner utilizes the explosion power of the explosive and theresilient power of the compression spring as a driving power for thepretensioner, it is practically difficult to intensify the webbingtightening power and a quantity of webbing tightening activity with thepretensioner.

In case that the gas generator is used for the pretensioner as a drivingpower source for the webbing tightening activity, a quantity ofexplosive should be increased in order to intensify the webbingtightening power but the increasing of the quantity of explosive isstrictly limited from the viewpoint of safe treatment of the explosiveand safety of the pretensioner. To increase a quantity of explosive andintensify the gas pressure of the explosive, it is necessary that acontainer is disposed in the pretensioner for receiving the gasgenerator in the container with a sufficiently high strength against thepressure of the gas generated by explosion of an explosive. In thisconnection, a problem is that a production cost of the pretensioner israised up due to the necessity for reinforcing other components ratherthan the container.

In case that the resilient power of the compression spring is utilizedas a driving power for the pretensioner, to intensify the webbingtightening power, it is necessary that the compression spring isdesigned with large dimensions and a spring constant of the compressionspring is increased. This leads to the result that other components suchas a weight, a trigger unit or the like should additionally bereinforced with certain additional means. Thus, there arises a problemthat a production cost of the pretensioner is undesirably raised up.

In addition, to assure that the webbing is more intensely tightened, itis generally required that the pressure of gas in the cylinder iselevated in the rear half of tightening time when the tension applied tothe webbing in increased, in order to intensify the webbing tighteningpower for the seat belt tightening device. With the aforementioneddriving unit having the explosion power of an explosive utilizedtherefor, however, it is practically difficult to properly control anintensity of webbing tightening power and a driving time of the webbing,because the gas pressure is quickly increased immediately after theexplosive is exploded, and thereafter, it is gradually decreased. Forthis reason, it is difficult to obtain adequate webbing tighteningproperties with the seat belt tightening device, and moreover, it isdifficult that the seat belt tightening device exhibits excellentpassenger restriction performances. Similarly, with the aforementioneddriving unit having the explosion power of the elastic force of thespring, it is practically difficult to properly control an intensity ofwebbing tightening power and a driving time of the webbing, because theelastic force of the spring is the highest at a setting position, andthereafter, it is gradually decreased.

The present invention has been made in consideration of theaforementioned background and its object resides in providing a seatbelt apparatus including a plurality of inexpensive pretensionerswherein the seat belt apparatus makes it possible to easily increase anintensity of webbing tightening power and a quantity of webbingtightening activity, and moreover, it assures adequate webbingtightening performances wherein each passenger sitting on a seat in avehicle can firmly be restricted with high safety.

SUMMARY OF THE INVENTION

To accomplish the above object, the present invention provides a seatbelt tightening device wherein a piston displaceably received in acylinder is driven at the time of an occurrence of emergency, causing ahigh intensity of tension to be applied to a power transmission memberconnected to the piston so as to enable the loosened state of a seatbelt to be eliminated by stretching a webbing with the power given bythe power transmission member, wherein the seat belt tightening deviceis characterized in that a plurality of gas generators each adapted todrive the piston by the explosion pressure generated by explosion of anexplosive filled in each of the gas generators are arranged on the baseend side of the cylinder so that the piston is driven by the expansionpressure of gas generated in each of the gas generators.

According to one aspect of the present invention, there is provided aseat belt apparatus wherein one end of a webbing is connected to aretractor, the other end of the webbing is connected to a vehicle bodyat the lower end position of the latter via a through-anchor, and athrough tongue disposed at the intermediate portion of the webbingbetween an anchor plate and the through-anchor is connected to a bucklestanding upright from the substantially central part of the vehicle bodyso as to allow each passenger to be reliably restricted on a seat in avehicle, wherein the seat belt apparatus is characterized in that aplurality of pretensioners each including a driving unit are arrangedfor the seat belt apparatus, the driving unit serving to eliminate theloosened state of a seat belt by retractively driving the webbing at thetime of an occurrence of emergency such as vehicle collision or thelike.

In addition, according to other aspect of the present invention, thereis provided a seat belt apparatus of the foregoing type, wherein theseat belt apparatus is characterized in that a plurality ofpretensioners are arranged for the seat belt apparatus, each of thepretensioners being adapted to operate in such a manner that a windingshaft for the retractor is rotated by driving a wire of which one end isconnected to the winding shaft and of which end is operatably pulled atthe time of an occurrence of emergency such as vehicle collision or thelike, the winding shaft being rotated in such a direction that theloosened state of the seat belt can be eliminated.

The seat belt tightening device constructed according to the presentinvention assures that the driving power for winding the seat belt canbe intensified by elevating the explosion pressure of an explosiveexerted on the piston without any necessity for increasing a quantity ofexplosive filled in each gas generator. In addition, the seat belttightening device makes it possible to control an intensity of webbingtightening power and a duration time of the webbing tightening power byproperly controlling the time when each gas generator is ignited.

With the seat belt apparatus constructed according to the presentinvention, an intensity of webbing tightening power can be increased bysimultaneously actuating a plurality of pretensioners without anynecessity for intensifying the driving power generated by a driving unitfor each pretensioner. In addition, the seat belt apparatus makes itpossible to properly control an intensity of webbing tightening powerand a duration time of the tightened state by adequately controlling thetime of actuation of each of the pretensioners.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially exploded front view of a retractor including apretensioner constructed according to a first embodiment of the presentinvention, particularly showing essential components constituting theretractor.

FIG. 2 is an enlarged sectional view of the pretensioner shown in FIG.1, particularly showing essential components constituting thepretensioner.

FIG. 3 is an enlarged sectional view of a pretensioner constructedaccording to a second embodiment of the present invention, particularlyshowing essential components constituting the pretensioner.

FIG. 4 is an enlarged sectional view of a pretensioner constructedaccording to a third embodiment of the present invention, particularlyshowing essential components constituting the pretensioner.

FIG. 5 is a partially exploded front view of a seat belt retractorconstructed according to a fourth embodiment of the present inventionwherein two pretensioner are attached to the seat belt retractor.

FIG. 6 is a fragmentary enlarged sectional view of the pretensionerstaken along line VI--VI in FIG. 5.

FIG. 7 is a perspective view of a seat belt apparatus constructedaccording to a fifth embodiment of the present invention.

FIG. 8 is a vertical cross sectional view showing the mechanical typepretensioner shown in FIG. 7.

FIG. 9 is a partially exploded front view of a conventional, retractorincluding a pretensioner, particularly showing essential componentsconstituting the retractor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail hereinafter withreference to the accompanying drawings which illustrate preferredembodiments thereof. A first embodiment according to the presentinvention will now be described in detail with reference to FIGS. 1 and2.

FIG. 1 is a partially exploded front view of a retractor including apretensioner constructed according to a first embodiment of the presentinvention. A retructor having a pretensioner designated by referencenumeral 1 includes a winding reel 17 having a webbing 16 woundthereabout in the laminated structure in such a manner as to freely windand unwind the webbing 16, and a pretensioner 3 serving as a seat belttightening device for rotating a winding shaft in such a direction thatthe loosened state of a seat belt can be eliminated is arranged on oneside wall of a retractor base 18 having a substantially U-shapedsectional contour. The pretensioner 3 serves to apply a certainintensity of tension to a wire 7 wound about a pulley (not shown)mounted on a winding shaft at one end of the latter to serve as a powertransmission member, allowing the winding shaft to be rotated in thewebbing winding direction. With this construction, the wire 7 is quicklypulled upwardly at the time of an occurrence of emergency so as toforcibly rotate the pulley integrally mounted on the winding shaft in awebbing winding direction, whereby the webbing 16 extending about apassenger's body is quickly retracted in the retractor 1. In addition,the pretensioner 3 includes a driving unit 4 for applying a certainintensity of tension to the wire 7. (One example of the connectingstructure between the wire and the winding shaft will be described in afifth embodiment and shown in the FIGS. 5 and 6).

As shown in FIG. 2, the driving unit 4 is composed of a piston 6connected to one end of the wire 7, a cylinder 5 .Iadd.(first chamber).Iaddend.in which the piston 6 is slidably received, a substantiallycylindrical housing 15 .Iadd.(second chamber).Iaddend., which extends ina direction perpendicular to the longitudinal direction of the cylinder5, connectably communicated with the base end side of the cylinder 5 anda opposing pair of gas generators 8 and 9 .Iadd.accommodated inaccommodating portions of the housing 15 and .Iaddend.arranged atopening portions on the opposite sides of the housing . .5.!..Iadd.15.Iaddend.. An opening portion 19 is formed at the central partof the housing 15 as seen in the longitudinal direction of the latter,and the wire 7 is inserted through a hole 20 which is formed through thehousing 15 at the position located opposite to the opening portion 19.

Both the gas generators 8 and 9 are constructed with a same structure insuch a manner that an explosive 11 and a heat generating element 10 ofan ignition heater are received in a case 12 of each gas generatorsealably fitted into the housing 15. Signal lines 13 and 14 electricallyconnected to a control circuit (not shown) are connected to the gasgenerators 8 and 9 so that the ignition heater in the case 12 areindependently turned on in response to a detection signal outputted fromvehicle acceleration detecting means such as an acceleration sensor orthe like adapted to detect an occurrence of emergency such as vehiclecollision or the like. With this construction, it is possible toadequately control an ignition time when each of the gas generators 8and 9 is ignited.

Next, a mode of operation of the retractor 1 including the pretensionerconstructed in the aforementioned manner will be described below.

While a vehicle runs at a normal cruising speed, the pretensioner 3 isnot brought in operative engagement with the winding shaft. Thus, thewinding shaft can freely be rotated by the webbing 16. This makes itpossible to wind the webbing 16 about the winding shaft by the resilientpower of a winding spring (not shown), and moreover, unwind it againstthe resilient force of the winding spring.

When a certain magnitude of deceleration occurs with the vehicle due toquick braking or the like, an emergency locking mechanism (not shown) inthe retractor is activated, resulting in the rotation of the windingshaft being prevented. Thus, the webbing 16 is not unwound from thewinding shaft any more but since the collision sensor does not outputany detection signal, the driving unit 4 for the pretensioner 3 is notactuated at all.

On the contrary, when a predetermined large magnitude of decelerationoccurs with the vehicle at the time of vehicle collision or the like,the collision sensor detects this deceleration to output a detectionsignal therefrom. Subsequently, when explosives in both the gasgenerators 8 and 9 in the driving unit 4 are simultaneously exploded inresponse to the foregoing detection signal, the piston 6 slidablyreceived in the cylinder 5 is quickly displaced in the upward direction(i.e., in the A arrow-marked direction in FIG. 2) by the expansion ofcombustion gas generated in both the gas generators 8 and 9. Thereafter,when the wire 7 is quickly pulled in the A arrow-marked direction by apredetermined magnitude of pulling power induced by the driving power ofthe piston 6, the winding shaft for the webbing 16 is rotated in thewebbing winding direction with the result that the webbing 16 extendingabout a passengers body is wound about the winding shaft until theloosened state of the seat belt is eliminated.

At this time, since the gas pressure of the combustion gas effective fordriving the piston 6 assumes a value equal to the value derived from acombination of the pressure of the combustion gas generated in the gasgenerator 8 with the pressure of the combustion gas generated in the gasgenerator 9, the gas pressure required for driving the piston 6 can beincreased without any necessity for increasing the gas pressure of thecombustion gas generated in each of the gas generators 8 and 9 in excessof the gas pressure derived from the conventional gas generator.Consequently, there is no need of increasing a quantity of explosive tobe filled in each of the gas generators 8 and 9, resulting in explosivehandling performances and safety of each gas generator to be maintainedduring an assembling operation or the like being not deteriorated. Inother words, the seat belt fastening device of the present inventionassures that each passenger can more intensely and quickly be restrictedon his seat in the vehicle with an increased intensity of webbingtightening power at an increased tightening speed while suppressing thedeterioration of explosive handling performances and safety of each gasgenerator with the result that safety of each passenger at the time ofvehicle collision can be improved with the seat belt fastening device.

The seat belt fastening device constructed according to the firstembodiment of the present invention has been described above withrespect to the case that both the gas generators 8 and 9 aresimultaneously activated in response to an ignition signal.Alternatively, an ignition signal may be outputted to each of the gasgenerators 8 and 9 with a time difference therebetween so as to enablethe time of applying the tightening power to the webbing 16 to bevariably controlled with an increased degree of freedom for obtainingrequired webbing tightening properties with the seat belt tighteningdevice.

In this modified case, first, the gas generator 8 is activated inresponse to a first ignition signal, and subsequently, the gas generator9 is activated in response to a second ignition signal withpredetermined time delay after the first ignition signal is transmittedto the gas generator 8. With such modification, combustion gas isgenerated in the gas generator 9 around at the time when the pressure ofthe combustion gas generated in the gas generator 8 starts to bereduced. Thus, the pressure of the combustion gas effective for drivingthe piston 6 can be endured for a predetermined period of tighteningtime, and moreover, the gas pressure in the cylinder 5 can be increasedfor the rear half of tightening time when the tension applied to thewebbing 16 is increased, resulting in the webbing tightening power beingintensified while maintaining excellent restricting performances of theseat belt tightening device.

Next, a driving unit for a seat belt tightening device constructedaccording to a second embodiment of the present invention will bedescribed below with reference to FIG. 3.

FIG. 3 is a sectional view of a driving unit 21 for the seat belttightening device of the present invention. The driving unit 21 iscomposed of a piston 6 connected to one end of a wire 7, a cylinder 5 inwhich the piston 6 is slidably received, a substantially cylindricalhousing 25 connectably communicated with the base end side of thecylinder 5 and an opposing pair of gas generators 22 and 23. The baseend of the cylinder 5 is fixed to an opening portion 26 formed throughthe housing 25 at the position offset from the middle point of thehousing 25, and the wire 7 is inserted through a hole 27 locatedopposite to the opening portion 26.

The gas generator 22 is constructed in the same manner as the generators8 and 9 in the first embodiment and a signal line 24 electricallyconnected to a control circuit (not shown) is connected to the gasgenerator 22. In contrast with the gas generator 22, a signal lineelectrically connected to the control circuit is not connected to thegas generator 23. In this embodiment, after the gas generator 22 isignited in response to a detection signal outputted from vehicleacceleration detecting means such as an acceleration sensor or the likeadapted to detect vehicle collision or the like, the gas generator 23 issubsequently exploded by the function of shock and explosion pressureinduced by the gas generator 22 with some time delay from the ignitiontime of the gas generator 22. Thus, the pressure of the combustion gaseffective for driving the piston 6 can be endured for a predeterminedperiod of tightening time, and moreover, the gas pressure in thecylinder 5 can be increased for the rear half of tightening time whenthe tension applied to the webbing 16 is increased, resulting in thewebbing tightening power being intensified while maintaining excellentrestricting performances of the seat belt tightening device.

In case that the driving unit 21 is modified in the above-describedmanner according to the second embodiment of the present invention,there is no need of disposing any special delaying unit for delaying theignition time of the gas generator 23 from that of the gas generator 22.Consequently, the structure of the seat belt tightening device can besimplified while suppressing undesirable cost increase.

Next, a driving unit for a seat belt tightening device constructedaccording to a third embodiment of the present invention will bedescribed below with reference to FIG. 4.

FIG. 4 is a sectional view of a driving unit 31 for the seat belttightening device of a third embodiment according to the presentinvention. The driving unit 31 is composed of a piston 6 connected toone end of a wire 7, a cylinder 5 in which the piston 5 is slidablyreceived, a substantially cylindrical housing 36 connectablycommunicated with the base end side of the cylinder 5 and a pair of gasgenerators 32 and 33 arranged in insert portions 37 and 38 of thehousing 36.

The base end of the cylinder 5 is fixed to an upper opening portion ofthe housing 36, and the wire 7 is inserted through a hole 39 on thebottom of the housing 36 located opposite to the upper opening portionof the same. The insert portion 37 is communicated with an openingportion formed through the bottom of the housing 36, while the insertportion 38 is communicated with an opening portion formed through theside wall of the housing 36 at the position in the vicinity of the upperopening portion of the housing 36. As is apparent from the drawing, boththe insert portions 37 and 38 are designed in the form of a pair ofsubstantially cylindrical projections which are projected from theopening portions thereof in the slantwise downward direction (that is,which are inclined at a predetermined angle with respect to thelongitudinal direction of the cylinder 5) while extending in parallelwith each other, and the gas generators 32 and 33 are immovably receivedin the insert portions 37 and 38.

Both the gas generators 32 and 33 are designed with a same structure,and signal lines 34 and 35 electrically connected to a control circuit(not shown) are connected to the gas generators 32 and 33 so as toenable both the gas generators 32 and 33 to be independently ignited inresponse to detection signals outputted from vehicle accelerationdetecting means such as an acceleration sensor or the like adapted todetect vehicle collision or the like. Thus, the ignition time of each ofthe gas generators 32 and 33 can adequately be controlled with the aidof the control circuit.

In this embodiment, first, the gas generator 32 is ignited, andsubsequently, the gas generator 33 is ignited with predetermined timedelay from the ignition time of the gas generator 32. Thus, combustiongas is generated in the gas generator 33 around at the time when thepressure of the combustion gas generated in the gas generator 32 startsto be reduced. Thus, the pressure of the combustion gas effective fordriving the piston 6 can be endured for a predetermined period oftightening time, and moreover, the gas pressure in the cylinder 5 can beenlarged for the rear half of tightening time when the tension appliedto the webbing 16 is increased, resulting in the webbing tighteningpower being intensified while maintaining excellent restrictingperformances of the seat belt tightening device.

In case that the driving unit 31 is modified in the above-describedmanner according to the third embodiment of the present invention, sinceboth the gas generators 32 and 33 are arranged merely on the right-handside of the cylinder 5 as seen in the drawing, they are not projectedoutside of the cylinder 5 on the opposite sides of the latter, wherebythe pretensioner of the seat belt tightening device can be designed withsmall dimensions. Consequently, the retractor having the pretensionerattached thereto in the above described manner can easily be fitted to avehicle body.

It should of course be understood that the present invention should notbe limited only to the aforementioned three embodiments but variouschange or modification may be made without departure from the scope ofthe present invention as defined by the claim clause. The presentinvention has been described above with respect to the case that theseat belt tightening device constructed in the above-described manner isfitted to the retractor. Alternatively, the present invention mayequally be applied to a seat belt tightening device including a bucklewhich is instantaneously retracted in the webbing winding direction, asdescribed later. In addition, igniting means for both the gas generatorsshould not be limited only to ignition signals outputted from theaforementioned electrical detecting means. Alternatively, igniting meanshaving a substance of inertia employed therefor may be substituted forthe foregoing electrical igniting means.

In addition, the structure of the retractor including a pretensionershould not be limited only to the aforementioned types. Alternatively,various other type may be employed in place of the aforementioned ones.

FIG. 5 and FIG. 6 show a retractor 51 having two pretensioners attachedthereto for a so-called three point type seat belt apparatus constructedaccording to the fourth embodiment of the present invention. Theretractor 51 includes a winding reel 67 about which a webbing 64 iswound in the laminated structure, and the winding reel 67 is normallybiased by the resilient power of a winding spring (not shown) connectedto a winding shaft 52 for the winding reel 67 in such a direction thatthe webbing 64 is wound thereabout. At the time of an occurrence ofemergency such as vehicle collision or the like, an emergency lockingmechanism (not shown) is actuated so as not to allow the webbing 64 tobe unwound at all by preventing the winding shaft 52 from being rotatedfurther.

A first pretensioner 68 for rotating the winding shaft 52 in thedirection of eliminating the loosened state of a seat belt is arrangedon a left-hand side wall 53a of a retractor base 53 of the retractor 51having a substantially U-shaped sectional contour, while a secondpretensioner 69 having the substantially same structure as that of thefirst pretensioner 68 is arranged outside of a sub-frame 74 (i.e.,leftward of the subframe 74 as seen in FIG. 6). Both the firstpretensioner 68 and the second pretensioner 69 are covered with a commonhousing (not shown). The sub-frame 74 is fixedly secured to the sidewall 53a of the retractor base 53 by tightening a plurality of setscrews 77 while a plurality of spacers 75 each having a predeterminedlength is interposed between the side wall 53a of the retractor base 53and the sub-frame . .75.!. .Iadd.74.Iaddend..

The second pretensioner 69 arranged on the sub-frame 74 is composed of aplate 54 having a hole 54b formed so as to allow the left-hand end partof the winding shaft 52 to be inserted therethrough, a pawl wheel 70fixedly mounted on the winding shaft 52, a pawl member 56 turnablysupported on the plate 54 to turn about a support pin 58, a wire 61wound about the plate 54 while one end of the wire 61 is connected tothe pawl member 56, and a driving unit 66 connected to other end of thewire 61.

The hole 54b is formed through the plate 54 having a circular contour atthe central part of the latter so as to allow the left-hand end part ofthe winding shaft 52 to inserted through the hole 54b. A pair ofradially extending flange portions 54d are formed on the outerperipheral edge of the plate 54, while a pair of radially extending wirewinding portions 54c are formed on the left-hand side of the plate 54while projecting outside of the plate 54. A pair of conical engagementprojections 54a adapted to be engaged with a pair of holes 74b areformed on the flange portions 54d, and a pin insert hole 54e is formedthrough one of the flange portions 54d so as to turnably support thepawl member 56 to turn about the support pin 58 therethrough.

The plate 54 is rotatably supported on a bush 59 press-fitted into ahole 74a formed through the sub-frame 74. Since the plate 54 is normallybiased toward the sub-frame 74 by the resilient force of a cup washer 60interposed between the bush 59 and the plate 54, the conical engagementprojections 54a are brought in engagement with the holes 74b as theplate 54 is rotated With this construction, the plate 54 is normallysupported in such a manner as to prevent it from being rotated, but whena rotational power having an intensity in excess of a predetermined oneis exerted on the plate 54, the conical engagement projections 54a aredisengaged from the holes 74b against the resilient force of the cupwasher 60. At this time, the plate 54 becomes rotatable.

A plurality of teeth 70a are formed around the outer periphery of thepawl wheel 70 which is fitted onto the left-hand end part of the windingshaft 52 while it is fixedly secured to the winding shaft 52 bytightening a bolt 63 with the aid of a washer 62, whereby the pawl wheel70 is rotated together with the winding shaft 52.

The pawl member 56 includes an engagement portion 56a adapted to beengaged with each tooth 70a, a through hole 56b through which thesupport pin 58 is inserted while it is fixed to the plate 54 after it isinserted through the hole 56b, and a connecting portion 56c having oneend of the wire 61 connected thereto, whereby the pawl member 56 isturnably supported on the plate 54 adjacent to the pawl wheel 70. Inaddition, the pawl member 56 is normally biased by the resilient forceof a coil spring 57, of which one end is fixed to the pawl member 56 andof which other end is engaged with an engagement projection 54f, in sucha rotational direction that the engagement portion 56a is disengagedfrom the pawl wheel 70.

One end of the wire 61 is connected to the connecting portion 56c of thepawl member 56 via a wire end 65. As is best seen in FIG. 5, the wire 61is caused to extend in the upward direction after it is wound about thewire winding portion 54c by a predetermined number of turns. The otherend of the wire 61, i.e., the uppermost end of the same is connected toa piston (not shown) of the driving unit 66.

The driving unit 66 is electrically connected to a collision sensorwhich serves to output a detection signal when a deceleration having amagnitude in excess of a predetermined one occurs after the time of anoccurrence of vehicle collision. In response to the detection signal, agas generator (not shown) disposed in the driving unit 66 generates gasof an explosive in a cylinder so as to slidably displace a piston in thecylinder by the gas pressure. As the piston is displaced in that way,the wire 61 is stretchably unwound in the upward direction (in the Xarrow-marked direction as seen in FIG. 5).

The first pretensioner 68 is arranged on the side wall 53a of theretractor base 53 in such a manner that a pawl wheel 55 corresponding tothe pawl wheel 70 in the second pretensioner 69 is rotated together withthe winding shaft 52 through a key 78 which is fitted on the outerperipheral surface of the winding shaft 52. The first pretensioner 68 isdesigned in the same manner as the second pretensioner 69 with theexception that a hole 53b formed through the side wall 53a of theretractor base 53 is brought in engagement with a conical engagementprojection 54a on the plate 54 as the latter is rotated. A driving unit66 for the first pretensioner 68 is constructed such that a piston (notshown) slidably received in the driving unit 66 is displaced in thedownward direction (i.e., in the Y arrow-marked direction as seen inFIG. 5) with an angular offset of 180 degrees relative to the drivingunit 66 for the second pretensioner 69. Other components rather than thedriving unit 66 are represented by same reference numerals as those ofthe second pretensioner 69. Thus, repeated description on thesecomponents will not be required.

With the retractor 51 constructed in the above-described manner, thedriving units 66 for both the first and second pretensioners 68 and 69can independently be actuated in response to a detection signaloutputted from the collision sensor electrically connected to a controlcircuit (not shown) which serves to adequately control the actuationtime of each of both the first and second pretensioners 68 and 69.

Next, a mode of operation of the retractor 51 constructed in theabove-described manner will be described below.

While a vehicle runs at a normal cruising speed, the pawl members 56 onboth the first and second pretensioners 68 and 69 are not engaged withthe pawl wheels 55 and 70 so that the winding shaft 52 can freely berotated. Thus, a webbing 64 can be wound about the winding shaft 52 bythe resilient power of a winding spring. Otherwise, it can be unwoundfrom the winding shaft 52 against the resilient power of the windingspring.

When a considerably large magnitude of deceleration occurs with thevehicle due to quick braking or the like, an emergency locking mechanism(not shown) in the retractor 51 is actuated to prevent the rotation ofthe winding shaft 52. At this time, since further unwinding of thewebbing 14 from the winding shaft 52 is not permitted and the collisionsensor does not output any collision signal therefrom, the driving units66 of both the first and second pretensioners 68 and 69 are notactuated.

On the contrary, when a very large magnitude of deceleration occurs withthe vehicle due to an occurrence of emergency such as vehicle collisionor the like, the collision sensor detects this deceleration and outputsa detection signal which in turn is simultaneously transmitted to boththe first and second pretensioners 68 and 69 as an ignition signal,causing explosion gas to be filled in the cylinders of both the drivingunits 66, whereby the piston in the cylinder of the driving unit 66 inthe second pretensioner 69 is displaced in the upward direction (i.e.,in the X arrow-marked direction as seen in FIG. 5), while the piston inthe cylinder of the driving unit 66 in the first pretensioner 68 isdisplaced in the downward direction (i.e., in the Y arrow-markeddirection as seen in FIG. 5). Consequently, the wire 61 of the secondpretensioner 69 is quickly pulled with a predetermined intensity ofpulling power in the X arrow-marked direction, while the wire 61 of thefirst pretensioner 68 is quickly pulled with a predetermined intensityof pulling power in the Y arrow-marked direction. At this time, sincethe plates 54 of both the first and second pretensioners 68 and 69 areheld in the immovable state without any rotation thereof, the pullingpower of the wires 61 applied to the pawl members 56 via the connectingportions 56c turnably drives the pawl members 56 against the resilientpower of the coil springs 57 in the counterclockwise direction as seenin FIG. 5, whereby the engagement portions 56a of the pawl members 56are brought in meshing engagement with a tooth 55a on the pawl wheel 55and a tooth 70a on the pawl wheel 70. Since the wires 61 for turnablydriving the pawl members 56 are connected directly to the pawl members56, the meshing engagement of the engagement portions 56a with the pawls55a and 70a is reliably achieved with both the first and secondpretensioners 68 and 69.

As the wires 61 are pulled further, the rotational power having anintensity in excess of a predetermined one is exerted on the plates 54via the support pin 58, resulting in the engagement projections 54a onthe plates 54 being disengaged from the holes 53b and 74b against theresilient force of the cup springs 60. Thus, the plates 54 are rotatedin the Z arrow-marked direction as seen in FIG. 5. At this time, sincethe pawl members 56 are still engaged with the pawl wheels 55 and 70,both the pawl wheels 55 and 70 are rotated together with the plates 54by the driving power given by the wires 61 in the Z arrow-markeddirection.

As a result, since the winding shaft 52 is rotated in the direction ofwinding the webbing 64 about the winding reel 67, the webbing 64 istightened so as to enable the loosened state of the webbing 64 to beeliminated.

Specifically, since the winding power effective for winding the webbing64 in that way is intensified by simultaneously rotating the windingshaft 52 by the driving units 66 of both the first and secondpretensioners 68 and 69, there is no need of increasing an intensity ofdriving power generated by each driving unit 66 much more than that ofthe conventional seat belt apparatus. Consequently, there is no need ofincreasing a quantity of explosive required for activating each drivingunit 66, there is no need of fitting a container to the seat beltapparatus for receiving a gas generator therein with a sufficiently highstrength enough to stand against a higher pressure than that of theconventional seat belt apparatus, and moreover, there is no need ofreinforcing other components rather than the container with certainadditional means. Thus, each passenger can intensely be restricted onhis seat in the vehicle with an increased intensity of webbingtightening power while suppressing any increase of a production cost ofthe seat belt apparatus, resulting in safety of each passenger at thetime of an occurrence of vehicle collision being improved.

The present invention has been described above with respect to the casethat both the first and second pretensioners 68 and 69 aresimultaneously actuated in response to an ignition signal outputted fromthe collision sensor. Otherwise, the present invention may be modifiedin such a manner that the webbing tightening time is controlled byactivating both the first and second pretensioners 68 and 69 in responseto ignition signals outputted from the collision sensor with a certaintime difference therebetween.

In this modified embodiment, it is possible to stepwise control anintensity of webbing tightening power by actuating the firstpretensioner 68 by detection of a primary collision, and subsequently,actuating the second pretensioner 69 by detection of a secondary vehiclecollision. In addition, it is possible to increase a quantity of webbingtightening activity by actuating the second pretensioner 69 aftercompletion of actuation of the first pretensioner 68. In this case,since the pawl member 56 of the first pretensioner 68 is disengaged fromthe corresponding pawl wheel 55 when the winding shaft 52 isrotationally driven by the second pretensioner 69 after completion ofthe winding operation with the first pretensioner 68, there does notarise a malfunction that rotational driving of the winding shaft 52 tobe achieved by the second pretensioner 69 is obstructed by the firstpretensioner 68.

Since both the pretensioners can independently be actuated in theabove-described manner in addition to the case that they aresimultaneously actuated, according to the present invention, the webbingtightening properties of the seat belt apparatus can adequately becontrolled.

In the aforementioned embodiment, pretensioners each having a samestructure are used for constructing the seat belt apparatus.Alternatively, pretensioners each having a different structure may becombined with each other.

A seat belt apparatus constructed according to a fifth embodiment of thepresent invention will be described below with reference to FIG. 7. Theseat belt apparatus shown in FIG. 7 belongs to a so-called three pointtype seat belt apparatus. One end of a webbing 64 is connected to a seatbelt retractor 81 having a pretensioner attached thereto, while otherend of the same is connected via a through-anchor 82 to an anchor plate84 disposed at the lower end part of a vehicle body. A passenger isrestricted on a seat in the vehicle by connecting a through-tongue 86disposed at the intermediate portion between the anchor plate 84 and thethrough-anchor 82 to a buckle 85 standing upright from the central partof the vehicle body. In this embodiment, by fitting a conventionalmechanical type pretensioner 83 to the buckle 85 in addition to apretensioner 87 for the retractor 81, the seat belt apparatus isconstructed in such a manner as to include two pretensions.

The pretensioner 87 for the retractor 81 belongs to a conventionalpretensioner (please refer FIG. 9) which serves to retract a webbing 64by instantaneously rotating a winding shaft of the retractor 81 when amagnitude of deceleration in excess of a predetermined one occurs withthe vehicle for some reason. On the other hand, the mechanical typepretensioner 83 includes a weight adapted to move on an occurrence ofacceleration due to shock or the like and a trigger unit for releasingthe restorative resilient power of a compression spring, a leaf springor the like held in the preliminarily biased state in operativeassociation with the weight, and serves to eliminate the loosened stateof the webbing 64 by instantaneously retracting the buckle 85 when amagnitude of deceleration in excess of a predetermined one occurs withthe vehicle.

FIG. 8 shows a vertical cross sectional view of one example of theabove-mentioned mechanical type pretensioner 83. A L-shaped housing 101of the mechanical type pretensioner 83 has a hook shaped hollow bodywhich is provided with a horizontal portion 102 extending a substantialhorizontal direction and a vertical portion 103 extending in a upwarddirection relative to the horizontal portion 102 with an acute angle.The L-shaped housing 101 is fixedly mounted through a bolt member, as apart of vehicle body, to a rail portion mounted on the floor of thevehicle or a mounting surface upstanding relative to the floor thereof,through mounting holes 101c formed on a projecting portion 1b which isupwardly projected from the side wall 101a of the horizontal portion 102of the housing 101.

A ratchet 107a is provided with pawls in the form of continuous sawtoothwhich are formed on the inner side wall of the vertical portion 103 andare linearly extended at predetermined intervals in the longitudinaldirection of the vertical portion 103. A pawl block 108 is provided inthe vertical portion 103. The pawl block 108 is provided with a ratchet107b which is formed on the one side wall thereof and having pawls to beengaged with the pawls of the ratchet 107a. A leaf spring 113 is securedto the other side wall of the pawl block 108 which is opposed to the oneside wall on which the ratchet 107b is provided. The pawl block 108 isbiased by the leaf spring 113 with respect to a rear wall 101e of thevertical portion 103 in such a manner that the engagement state betweenthe ratchet 107a and the ratchet 107b is maintained.

The pawls of the ratchet 107a and 107b are directed in such a mannerthat the pawl block 108 is only movable in a retracting direction of thevertical portion 103.

As shown in FIG. 8, in this embodiment, the leaf spring 106 is of alaminated spring type which is constructed by three plates. However, theleaf spring 106 of the three plates laminated spring type can bereplaced with a leaf spring of a single leaf spring type in such amanner that a thickness and a width of the single leaf spring aredesigned so as to have a suitable function. The end portions 110a of thethree plates 106a, 106b and 106c of the laminated leaf spring 106 areuniformly arranged and are secured by a nut 121 and a bolt 120 whichpenetrates the tip end 104 of the horizontal portion 102 of the L-shapedhousing 101. The other end of each three plates 106a, 106b and 106c ismade free. A practical free end of the leaf spring 106 is the free endof the longest plate 106a and is indicated at 110b, as shown in FIG. 8.A slot 144 is formed at the free end 110b.

A buckle 85 is substantially disposed on the vertical portion 103 forreceiving and locking a metal fitting of the seat belt apparatus. A wire114 extending from the buckle 85 is secured to the upper portion of thepawl block 108. One end of a cable 111 is secured to the lower portionof the pawl block 108, and the other end of the cable 111 is fixedlysecured to the free end 110b of the leaf spring 106.

As shown in FIG. 8, a trigger apparatus 105 has a bent lever 140. Thesubstantial center portion of the bent lever 140 is pivotally supportedby a shaft 142 which is inwardly projected from a part of the housing101, and the lower portion of the bent lever 140 is forked downwardlyand is brought in contact with the upstanding projection 130 of theweight body 31. The upper portion of the bent lever 140 is inwardlyextended from the end of the lower portion by slightly bending at thecenter portion. A roller 141 is rotatably mounted on the shaft 143supported at the tip end of the upper portion of the bent lever 140, andis engaged with the slot 144 formed on the free end 110b of the leafspring 106. In the case where the weight body 131 of the triggerapparatus 105 is subjected to an acceleration at the time of anoccurrence of vehicle collision, the weight body 131 is moved in aB-direction and the roller 141 is moved in a V-direction toward theoutside of the slot 144 so as to release the free end 110b of the leafspring 106. Thereby, the buckle 85 is pulled by the leaf spring 106.

With this construction, when a very large magnitude of decelerationoccurs with the vehicle at the time of an occurrence of emergency suchas vehicle collision or the like, a collision sensor detects thisdeceleration and outputs a detection signal therebetween. In response tothis detection signal, the pretensioner 87 is actuated, and at the sametime, the mechanical type pretensioner 83 is also actuated because theweight moves to release the restorative resilient power derived fromspring means such as a compression spring, a leaf spring or the like.

Since the retracting power of the seat belt apparatus is intensifiedwhen it is retractively driven by the retractor 81 and the mechanicaltype pretensioner 83 at the substantially same time, there is no need ofincreasing an intensity of driving power generated by each driving unitmuch more than that of the conventional seat belt apparatus. Thus, eachpassenger can intensely be retracted on his seat by intensifying thewebbing tightening power without any increase of a quantity of explosivereceived in each driving unit as well as a spring constant of the springmeans. Consequently, safety of each passenger at the time of anoccurrence of emergency such as vehicle collision or the like cansubstantially be improved.

Similarly to the preceding embodiment, the time when the webbing 64 isretracted to generate the retracting power can properly be controlled byadequately delaying the ignition time of an explosive in thepretensioner 87 from the actuation time of the mechanical typepretensioner 83, whereby the webbing tightening properties of the seatbelt apparatus can adequately be controlled.

Further, since the seat belt apparatus constructed according to thisembodiment includes the pretensioner 87 for operatably rotating thewinding shaft of the retractor in response to an electrical signal andthe mechanical type pretensioner 83 for retractively driving the buckle,even in case that the pretensioner 87 can not be actuated due to anoccurrence of abnormality in the electrical system, it is possible toactuate the pretensioner 83. On the contrary, even in case that thepretensioner 83 can not be actuated due to some mechanical abnormality,it is possible to actuate the pretensioner 87. For this reason, eachpassenger can reliably be restricted on his seat in the vehicle.

With the seat belt apparatus constructed according to the presentinvention, since the webbing tightening power can be intensified bysimultaneously actuating a plurality of pretensioners without anynecessity for increasing an intensity of driving power to be generatedby a driving unit in each pretensioner, there is no need of intensifyingthe driving power of each driving unit, and moreover, there is no needof reinforcing components constituting the driving unit with certainadditional means. Thus, each passenger can intensely be restricted onhis seat in the vehicle by intensifying the webbing tightening powerwhile suppressing increase of a production cost of the seat beltapparatus, whereby safety of each passenger at the time of an occurrenceof vehicle collision can substantially be improved. In addition, sinceit is possible to properly control an intensity of webbing tighteningpower and a duration time of the tightened state by adequatelycontrolling the actuation timing relationship among a plurality ofpretensioners, acceptable webbing tightening performances can beobtained with the seat belt apparatus.

Conclusively, the present invention has provided a seat belt apparatushaving high safety and excellent properties wherein it is possible toeasily increase an intensity of webbing tightening power and a quantityof webbing tightening activity, and moreover, each passenger canreliably be restricted on his seat in the vehicle by employing aplurality of inexpensive pretensioners.

What is claimed is:
 1. A seat belt tightening device comprising:aretract or base; a winding reel rotatably supported on said retractorbase for freely winding and withdrawing a webbing thereabout; acylinder; a piston slidably received in said cylinder; a driving forcetransmitting member having a first end connected with said piston and asecond end opposed to said first end; at least two gas generatorsmounted on a base end side of said cylinder for driving said piston withan expansion of combustion gas generated in said gas generators; acoupling means for coupling said second end of said transmitting memberwith said winding reel when said gas generators are actuated, therebysaid webbing is wound on said winding reel by rotating said winding reelbeing subjected to a driving force of said piston connected to saidtransmitting member which is coupled with said winding reel through saidcoupling means; and a cylindrical housing connected and communicatedwith said base end side of said cylinder, said cylindrical housing beingextended in a direction perpendicular to a longitudinal direction ofsaid cylinder, said gas generators being disposed at both ends of saidcylindrical housing, respectively.
 2. A seat belt tightening deviceaccording to claim 1, wherein each said gas generators includes anexplosive, a heat generating element embedded in said explosive, and asignal line electrically connected to said heat generating element,wherein said heat generating elements of said gas generators areindependently ignited.
 3. A seat belt tightening device according toclaim 2, wherein said heat generating elements of said gas generatorsare different from each other in an ignition time.
 4. A seat belttightening device according to claim 1, wherein one of said gasgenerators is constructed with an explosive, a heat generating elementembedded in said explosive, and a signal line electrically connected tosaid heat generating element, and the other one of said gas generatorsis exploded by the function of shock and explosion pressure induced bysaid one of the gas generators.
 5. A seat belt tightening devicecomprising:a retractor base; a winding reel rotatably supported on saidretractor base for freely winding and withdrawing a webbing thereabout;a cylinder; a piston slidably received in said cylinder; a driving forcetransmitting member having a first end connected with said piston and asecond end opposed to said first end; at least two gas generatorsmounted on a base end side of said cylinder for driving said piston withan expansion of combustion gas generated in said gas generators; acoupling means for coupling said second end of said transmitting memberwith said winding reel when said gas generators are actuated, therebysaid webbing is wound on said winding reel by rotating said winding reelbeing subjected to a driving force of said piston connected to saidtransmitting member which is coupled with said winding reel through saidcoupling means; and a housing the upper opening portion of which isfixed to and is communicated with the base end of said cylinder, whereinsaid housing has at least two cylindrical insert portions which areinclined at a predetermined angle with respect to the longitudinaldirection of said cylinder, and said gas generators are respectivelymounted on the ends of said insert portions.
 6. A seat belt tighteningdevice according to claim 5, wherein said insert portions are extendedin parallel with each other, and said insert portions are extended in adirection away from said base end of said cylinder.
 7. A seat belttightening device according to claim 6, wherein an ignition time of eachof said gas generators is independently controlled so that one of saidgas generators which is disposed at the furthest position from the baseend of said cylinder is firstly ignited.
 8. A seat belt tighteningdevice according to claim 6, wherein said insert portions are arrangedon a side of said cylinder. .Iadd.
 9. A seat belt tightening deviceincluding a retractor base, a winding reel rotatable supported on saidretractor base, and a webbing connected to said winding reel, in whichthe seat belt tightening device eliminates the looseness of said webbingby driving said winding reel in a retracting direction to apply atension to said webbing in an emergency, the seat belt tightening devicecomprising:a driving unit supported by said retractor base, said drivingunit being partitioned into first and second compartments that arecommunicated with each other; a driving member disposed in the firstcompartment for driving said winding reel; a coupling member forcoupling said driving member with said winding reel; and at least twogas generators arranged in said second compartment independently of eachother, said gas generators each including an explosive for driving saiddriving member by an explosion pressure generated by said explosive,said explosives of said gas generators being capable of being operatedindependently of each other, wherein said second compartment is providedwith a plurality of accommodating portions for accommodating said gasgenerators independently of each other. .Iaddend..Iadd.10. A seat belttightening device including a retractor base, a winding reel rotatablysupported on said retractor base, and a webbing connected to saidwinding reel, in which the seat belt tightening device eliminates thelooseness of said webbing by driving said winding reel in a retractingdirection to apply a tension to said webbing in an emergency, the seatbelt tightening device comprising: a driving unit supported by saidretractor base, said driving unit being partitioned into first andsecond compartments that are communicated with each other; a drivingmember disposed in the first compartment for driving said winding reel;a coupling member for coupling said driving member with said windingreel; and at least two gas generators arranged in said secondcompartment independently of each other, said gas generators eachincluding an explosive for driving said driving member by an explosionpressure generated by said explosive, said explosives of said gasgenerators being capable of being operated independently of each other,wherein said second compartment is an elongated compartment, and saidgas generators are disposed at opposite ends of said second compartment..Iaddend..Iadd.11. A seat belt tightening device including a retractorbase, a winding reel rotatable supported on said retractor base, and awebbing connected to said winding reel, in which the seat belttightening device eliminates the looseness of said webbing by drivingsaid winding reel in a retracting direction to apply a tension to saidwebbing in an emergency, the seat belt tightening device comprising: adriving unit supported by said retractor base, said driving unit beingpartitioned into first and second compartments that are communicatedwith each other; a driving member disposed in the first compartment fordriving said winding reel; a coupling member for coupling said drivingmember with said winding reel; and at least two gas generators arrangedin said second compartment independently of each other, said gasgenerators each including an explosive for driving said driving memberby an explosion pressure generated by said explosive, said explosives ofsaid gas generators being capable of being operated independently ofeach other, wherein said second compartment comprises at least twoelongated insert portions, and said gas generators are respectivelymounted on one end of said insert portions. .Iaddend..Iadd.12. A seatbelt tightening device eliminating the looseness of a webbing by drivinga member connected to said webbing with a driving force of a drivingmember to apply a tension to said webbing in an emergency, the seat belttightening device comprising: a driving unit partitioned into first andsecond compartments that are communicated with each other, said drivingmember being disposed in said first compartment; at least two gasgenerators arranged in said second compartment independently of eachother, said gas generators each including an explosive for driving saiddriving member by an explosion pressure generated by said explosive; andmeans for operating the explosives of said gas generators with a timedifference therebetween. .Iaddend..Iadd.13. The seat belt tighteningdevice according to claim 12, in which said second compartment isprovided with a plurality of accommodating portions for accommodatingsaid gas generators independently of each other. .Iaddend.